The invention concerns a pressure-limiting valve to limit the pressure of hydraulic oil which can be admitted through two intakes, consisting of a control rod in a cylindrical housing equipped with the two intakes, which can be moved against spring force, which, when one intake is exposed to oil under high pressure, connects the other intake supplied with oil kept under low pressure to an outlet leading to the pressure-limiting valve.
Such a pressure-limiting valve is useful, for example, in a hydraulic motor, preferably a hydraulic axial piston motor, which is fed with oil under pressure in a closed circuit from an adjustable pump, preferably a slant piston axial adjustable pump, where the valve arrangement is pushed by the high-pressure side into a position in which the low pressure side is connected to the tank through the pressure-limiting valve, so that oil can be fed into the tank from the low-pressure side against the pressure provided by the pressure-limiting valve, and cool hydraulic oil for compensation can be fed into the circulation by the check valve.
A valve arrangement of this known type is described briefly using FIG. 1, which shows a partial section of a connection plate of a hydraulic axial piston motor. A 4/2-way valve 90 is screwed into a hole in the connection plate, which is provided with annular steps, whose control rod 91, which is movable against spring force and which is provided with 2 pistons, is pushed by the high pressure that lies either at hole 92 or hole 93 into a position in which always the other hole, which is provided with low pressure, is connected to the outlet 95 through the annular space 94 which lies between the pistons of the control rod, which opens into the intake side of the pressure-limiting valve 96, which is screwed into the hole 97 in the connection plate and which is provided with annular steps.
FIG. 2 shows a schematic diagram of the valves shown in FIG. 1 and combined with each other.
The known valve system is complex, since it consists of two valves combined with each other, each of which must be placed in its own hole, for example, in a connection plate, and which must be connected to each other.
The problem to be solved by the invention is therefore to create a combined valve of the type indicated at the beginning, which is marked by a simpler structure and which can be installed more simply.
According to the invention, this problem is solved by providing the control rod with an axial hole, in which a second control rod is movable against the force of at least one limiting spring that is adjusted to the pressure to be limited, and placing the first control rod in a position depending upon which of the two inputs is subjected to high pressure, in which position the second control rod connects the input that is exposed to low pressure to an outgoing opening while overcoming the force of the limiting spring.
The pressure-limiting valve combined with a multiple-way valve in accordance with the invention is outstanding due to the fact that it is housed in a single, essentially cylindrical housing, and therefore can be installed in a hole, for example, in a connection plate.
Preferably, the first control rod is provided with pistons and/or annular pistons in the area of its ends, where the cylinder chambers that are set off by them from the housing are in communication, each with one of the intakes, in such a manner that the intake subjected to high pressure pushes the control rod into a position in which the other intake comes into communication with the output opening of the second control rod, through the low pressure.
It is advantageous for the first control rod to be equipped with an axial pin extending through a coiled spring, which, on the basis of spring disks guided by the pin, between which it is clamped, then has a double effect, so that the outer spring disk is graced against a stop on the pin and the internal spring is braced against an annular step on the inside end of the pin and both spring disks rest against annular steps of the housing.
In a further embodiment of the invention, the second control rod is provided in the area of its ends with pistons and/or annular pistons, which form cylinder chambers with the axial hole of the first control rod, where, by moving the first control rod, one of the cylinder chambers is placed in communication with the intake provided with low pressure, and connects this cylinder chamber with the outlet opening by moving the second control rod.
The second control rod can be provided with annular chambers between the pistons or annular pistons at the end, and a center blocker which, in its rest position, closes the outflow opening, which annular chambers communicate with the cylinder chambers by means of holes.
It is advantageous if one side of the second control rod is provided with a double-action pressure spring placed on a pin in a manner corresponding to the first control rod.
The housing of the first control rod advantageously consists of two parts, which screw together in order to make possible simple assembly of the second control rod.